We plan to continue our studies on the radial disposition of the cross-bridges of thick filaments in glycerinated muscle using bifunctional cross-linking reagents and proteolytic enzymes to probe release of the cross-bridges from the thick filament surface. We will also continue our current experiments on the tritium exchange of glycerinated muscle fibers under activating and resting conditions. The purpose of these latter experiments is to determine whether or not the LMM-HMM hinge region of the myosin molecule undergoes a helix-coil transition during a contractile cycle thus generating the contractile force. We hope to establish the size and location of the segment involved in the proposed force-generating process by isolation of the labelled segment following the tritium exchange reaction. We will continue our experiments on the number of myosin molecules in the native thick filament of skeletal muscle using the Scanning Transmission Electron Microscope (STEM). This work is being carried out in collaboration with Dr. Michael Beer and his group. We are continuing our comparative studies on the thermal melting behaviors of the long S-2 subfragments isolated from frog and rabbit myosins with a view to determining whether the physiological working temperature of the muscle is reflected in the thermal stability of the LMM-HMM hinge region.